Kinetics and mechanism of the oxidation of disaccharides by CrVI
| Autor: | Juan M. Salas-Peregrín, Juan Carlos González, Viviana Roldán, Silvina Olivera, Nieves Casado, Sandra Signorella, Luis F. Sala, Silvia García, Juan Carlos Boggio, Mabel Santoro |
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| Rok vydání: | 2002 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 80:1676-1686 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v02-187 |
| Popis: | The oxidation of D-lactose, D-maltose, D-melibiose, and D-cellobiose by CrVI yields the corresponding aldobionic acid and Cr3+ as final products when an excess of reducing disaccharide over CrVI is used. The rate law for the CrVI oxidation reaction is expressed by d[CrVI]/dt = kH [disaccharide][CrVI], where the second-order kinetic constant, kH, depends on [H+]. The relative reactivity of the disaccharides with CrVI is expressed as follows: Mel > Lac > Cel > Mal, at 33°C. In acid medium, intermediate CrV forms and reacts with the substrate faster than CrVI. The EPR spectra show that five- and six-coordinate oxo-CrV intermediates are formed, with the disaccharide acting as bidentate ligand. Five-coordinate oxo-CrV species are present at any [H+], whereas six-coordinate ones are observed only at pH < 2, where they rapidly decompose to the redox products. In the pH 37 range, where hexa-coordinate oxo-CrV species are not observed, CrV complexes are stable enough to remain in solution from several days to several months.Key words: chromium, saccharides, kinetics, EPR. |
| Databáze: | OpenAIRE |
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